Introduction to Enzymes Flashcards
Explain how enzymes act as catalysts and how they operate to increase the rate of a chemical reaction
They act as biological catalysts as they are not chemically altered in the reaction but increase the rate of reaction.
They increase the rate of reaction by lowering the activation energy required for a chemical energy by stabilising the transitions state.
when does the velocity of a reaction increase?
If the substrate concentration is increased.
How is enzyme activity measured?
By increasing the substrate concentration over time and measuring the accumulation of products over time.
How and why is the Vmax calculated?
It is calculated because the max velocity of an enzyme is hard to achieve. It is done by plotting a double reciprocal of the data (Lineweaver-burke plot)
What is Michaelis-menten constant?
A constant used with the Vmax to determine the enzyme activity. It is defined as the substrate concentration required for the half the maximum velocity.
How does a low Km affect enzymes?
Allows it to work at lower concentrations of substrate.
How does a high Km affect enzymes?
It means it only works at high substrate concentrations
How is the Km and the Vmax determined from a linewearver-burke plot?
-1/Km is where the line intercepts x-axis.
1/Vmax is the Y intercept.
What are the two types of enzyme inhibitors?
Irreversible and Reversable.
How do irreversible inhibitors work?
They react with the enzyme and form a covalent adduct.
Explain how an irreversible inhibitor works using Aspirin as an example
aspirin irreversibly inhibits cyclooxygenase (COX-1). COX-1 catalyses the conversion of arachidonic acid (AA) to prostaglandin (H2). Aspirin reacts with a serine residue close to the active site preventing the substrate, arachidonic acid, from binding.
Explain how a competitive inhibitor works and give an example
A competitive inhibitor has a similar structure to the normal substrate so it competes for the active site with the normal substrate. Therefore the action of the enzyme is slower. Sulphonamides are similar to a structure called 4-aminobenzoic acid, and acid that bacteria use to generate folic acid. Therefore sulphonamides are effective antibiotics because they starve bacteria of folic acid.
How do competitive inhibitors effect the Vmax and Km
It increases the value of Km but the Vmax remains unchanged.
What is an allosteric inhibitor and how does it effect the Vmax and Km
Allosteric inhibitors bind to an allosteric site and change the shape of the active site meaning the substrate can no longer bind. The Vmax decreases and generally the Km increases.
Name the two types of allosteric inhibition
Mixed inhibition - affects binding and activity. Vmax decreases due to inhibition and Km increases due to decreased substrate affinity.
Non-competitive inhibition - affects activity but not substrate binding so Vmax decreases due to reduced efficiency but Km remains the same as substrate affinity is unchanged.
